The present invention relates to a circuit for a device to measure the flowrate of a fluid containing electrical charges which flows in a pipe section. Such a device includes (1) at least one electromagnet connected to a current source which generates a magnetic field through the pipe section, (2) at least two electrodes whose central imaginary connecting line passes through the flow stream in the region of the magnetic field to measure the potential resulting from the charge displacements in the flowing fluid, and (3) a timing circuit which periodically changes the strength of the excitation current from the current source to the electromagnet and switches a signal shunt which is connected between the electrodes and at least two signal memories which are connected to a correction circuit, which, from the signals stored in the memories, produces an output signal corresponding to the flowrate of the fluid in the pipe section which is only minimally dependent on the flow profile or the level of the fluid in the pipe section.
The known electromagnet described in DE-OS 27 43 954 can be deenergized or have its polarity reversed to change the magnetic field in the pipe section and thereby develop a correction function from the signals coming from the electrodes, with which it is possible to produce an output signal corresponding to the flowrate of the fluid in the pipe section which is essentially independent of the flow profile.
A similar circuit arrangement for a pipe section is known from EP-0451 308 Al, which contains two pairs of electrodes with which the level of the fluid in the pipe section can be determined and through a correction function develop an output signal which is essentially independent of the flow profile in the flow stream and/or the level of the fluid in the pipe section.